Elongate tubular devices, such as diagnostic or treatment catheters or sheaths may be provided for introduction into a patient's body, e.g., the patient's vasculature or other body lumens. For example, a catheter may have a distal portion configured to be introduced into a body lumen and advanced to one or more desired locations within the patient's body by manipulating a proximal end of the catheter.
To facilitate introduction of such a catheter, one or more wires, cables, or other steering elements may be provided within the catheter, e.g., that are coupled to the distal portion and may be pulled or advanced from the proximal end to deflect the distal portion. For example, a steering element may be provided that is intended to deflect the distal portion within a predetermined plane and/or into a desired curved shape.
Pull wires are a common way to impart deflection ability to such a catheter. However, there are a number of drawbacks associated with such pull wires. For example, a pull wire occupies a significant amount of space within the catheter body. In addition, a pull wire frequently needs to be reinforced, e.g., on the inside and outside of the braid or other reinforcement of the catheter, e.g., to prevent “pull through” or loosening when the pull wire is actuated by pushing or pulling, i.e., the resulting bending moment may cause the pull wire to separate layers of or tear at least partially through the wall of catheter, potentially splitting the catheter and/or decreasing the mechanical actuation ability of the pull wire. Further, a pull wire can make the torque properties of the catheter non-homogenous, making it difficult or impossible to torque the catheter when the pull wire is actuated, e.g., within a tortuous pathway. Further, auxiliary lumens, in particular those located in the wall of a large bore sheath, are difficult to manufacture with consistency due to difficulties with alignment, hand assembly, and the like.
Pull and push wire based deflection mechanisms in catheters also create a number of design and performance challenges. These challenges including but are not limited to 1) avoiding undesirable bending/deflection outside of the desired deflection area, 2) avoiding stiffening of the catheter greater than is desirable, 3) avoiding limitation on torque transmission to the distal portion of the device, 4) avoiding high deflection forces, and/or 5) achieving manufacturing flexibility for the position of the deflection segment.
With regards to torque transmission, this challenge depends on at least two important conditions that are present in almost all common catheter uses: 1) the catheter is generally not used in a substantially straight condition (typical paths from entry into the body to the final locations predominantly include moderate to severe tortuosity) and 2) the catheter needs to be able to transmit torque to direct a distal deflectable segment to an ideal location (e.g., deflection alone does not generally provide the navigability desired by the operator).
Torque transmission through even moderate tortuosity becomes a problem when the forces associated with the pull or push wire are asymmetrically loaded onto the cross-section of the catheter. Thus, as the catheter is torqued/rotated around its axis, the path length change that occurs in the cross-section of the catheter from the inside edge of the curve to the outside edge of the curve may interfere with the pull wire. For example, if the pull wire is in tension and is asymmetrically loaded in the periphery of the cross-section and is moving from an area inside the curve to outside the curve, the catheter will need to overcome the force of the pull wire that is “fighting” to stay in a shorter length condition. If the torque properties of the catheter are high and there is residual deflection or compressibility left in the system, the torque may overcome this and rotations can occur.
However, even in this best case scenario, there are two significant limitations. 1) The torque profile as a function of rotation is not constant; in other words, it is unstable and irregular. This problem is commonly known as “whip.” 2) The change in path length of the pull wire may cause the pull wire to pull more/harder and may cause the deflection or actuation amplitude to increase. Alternatively, catheters without sufficient torque characteristics remain “stuck” in a narrow band of rotation and are unable to overcome the “whip.” Continued rotation/torque of the devices may instead cause a torsional kink in the device rather than rotation of the distal tip.
With regards to undesirable deflection, in addition to being unsightly, the undesired deflection that occurs through simple eccentrically-located push/pull systems may be problematic in many clinical situations, primarily those in which the catheter is operating in an open space, such as those of the heart or large vessels. Although variations in stiffness may shift the balance of deflection to a specific area, even a very stiff catheter (as stiff as is known in the art) may still list to one side in a segment outside the specified deflection segment depending on whether push or pull of the activation element is being used. This causes, for example, the non-primary deflection section of the catheter (usually close behind the deflectable segment) to list to the side. This may significantly reduce the level of control that the operator has as each action causes a separate reaction the results of which sometimes mean the operator cannot find a suitable solution.
Similarly, simple eccentrically-located push/pull systems may require the non-deflection sections to be substantially stiffer. This may cause a number of problems including but not limited to 1) ability to track through the anatomy, 2) damage to the anatomy, 3) and/or adverse effect on positioning within a lumen or chamber.
Additionally, deflection forces are not just a function of catheter stiffness and friction; they are also a function of the lever arm radius. The position of these push/pull actuators is currently limited by the need to have the pull wire inside the braid (the deflection forces pull outward against the braid—otherwise the pull/push element is likely to break through the outer surface of the catheter.
Yet other problems may exist, which may be appreciated by those skilled in the art, including loss of sensitivity due to changes in the shaft (or, e.g., changes in the length of the shaft due to heat, humidity, compression or extension forces, etc.).
Accordingly, there is a need for improved catheters, sheaths, and other tubular devices and methods of their manufacture.